In the field of biochemistry, sugar chain molecules have recently attracted attention as the third major type of chain after nucleic acids and proteins. In particular, research has been conducted on their involvement in such processes as cell differentiation and malignant transformation, immune reactions and fertilization, and efforts are continuing to be made to develop these molecules into novel pharmaceuticals and medical materials.
In addition, since sugar chains are receptors for numerous toxins, viruses, bacteria and the like and are also attracting attention for use as cancer markers, similar efforts are continuing to be made in these fields as well in order to develop novel pharmaceuticals and medical materials.
However, although the importance of sugar chain research is recognized, due to their complex structure and diversity, research is progressing quite slowly in comparison with the first two types of chains in the form of nucleic acids and proteins.
Consequently, the need has arisen in recent years for methods capable of analyzing the structure of sugar chains rapidly, easily and with high accuracy, and sugar chains have been analyzed by various such methods, examples of which include high-performance liquid chromatography (HPLC), nuclear magnetic resonance, capillary electrophoresis (CE), mass spectrometry and lectin array-based analyses. In order to analyze sugar chains using these various techniques, it is necessary to first isolate and purify sugar chains from proteins, peptides, lipids and nucleic acids and the like contained in biological samples. In addition, although HPLC and CE are widely used from the viewpoints of quality of isolation, quality of reproducibility, quantitativity and high sensitivity, it is necessary to label the reducing terminal of a sugar chain by reductive amination and the like in order to obtain high sensitivity. However, these sugar chain purification and labeling procedures require both time and labor, and make it difficult to prepare a large number of samples at one time.
Various methods have been developed for analyzing sugar chains by fluorescent labeling (see, for example, Patent Documents 1, 2 and 3). However, since the labeling efficiency of these methods is not 100%, both labeled and unlabeled sugar chains are present in a single sample. Although this does not present a significant problem during fluorescence detection using HPLC or CE, there was the problem of peaks becoming excessively complex when analyzing sugar chains by mass spectrometry. In addition, in the case of poor labeling efficiency, there was also the possibility of the problem of decreased sensitivity even when analyzing by HPLC or CE.